The present invention relates to a seat construction in general, and more particularly to a fitting for adjustably connecting a backrest member to a seat member of a seat, especially a seat of an automotive vehicle.
The use of seats, particularly those in automotive vehicles, wherein the backrest can be adjusted forwardly or backwardly with reference to the seat cushion in order to accommodate the seat to the preferences of a user, is becoming more and more popular. It is known from the prior art to provide a fitting for connecting the backrest member to the seat cushion or seat member, which makes such adjustment possible. This known fitting comprises a ring gear mounted on the backrest member or on the seat member, and a spur gear accommodated within the ring gear and mounted on the other of the members, that is either the seat member or the backrest member. The outer diameter of the spur gear is smaller than the root diameter of the ring gear by at least the height of one tooth, and the number of teeth on the ring gear and on the spur gear differs by at least one.
This construction has the advantage that even in the event of extreme stresses acting upon the backrest member, there can be no unintentional disengagement of the teeth of the spur gear and the ring gear, and hence unintentional displacement of the backrest member, since such disengagement is possible only when a mechanism is utilized which is a part of the prior-art fitting and which must be specifically operated in order to disengage the teeth of the two gears from one another so that one gear can turn with reference to the other. However, in order to be able to operate this prior-art construction with ease it is necessary that a certain amount of play exist between the teeth of the spur gear and the meshing teeth of the ring gear which, when the backrest member is to be moved relative to the seat member will be in rolling engagement with one another as one of the gears turns with reference to the other. Given the fact that these gears are not usually made to very exacting tolerances, for economic reasons, the amount of play has been found in some instances to be relatively substantial. This will then have the result that, due to vibrations of the vehicle when the latter is in motion, there will be a chattering of the gears, and the backrest member may actually be visibly movable as a result of external forces, for instance when pressure is exerted upon it.